Animate a circle with the growth of <path> on scroll

Question

Question updated

This what I have done so far.

It works fine but I want to do an animation which is little much complicated for me.

// Get the id of the <path> element and the length of <path>
var myline = document.getElementById("myline");
var length = myline.getTotalLength();

// The start position of the drawing
myline.style.strokeDasharray = length;

// Hide the triangle by offsetting dash. Remove this line to show the triangle before scroll draw
myline.style.strokeDashoffset = length;

// Find scroll percentage on scroll (using cross-browser properties), and offset dash same amount as percentage scrolled
window.addEventListener("scroll", myFunction);

function myFunction() {
  // What % down is it?
  var scrollpercent = (document.body.scrollTop + document.documentElement.scrollTop) / (document.documentElement.scrollHeight - document.documentElement.clientHeight);
  // Length to offset the dashes
  var draw = length * scrollpercent;

  // Reverse the drawing (when scrolling upwards)
  myline.style.strokeDashoffset = length - draw;
}

body {
  height: 2000px;
  background: #f1f1f1;
}

#mySVG {
  position: fixed;
  top: 15%;
  width: 100vw;
  height: 100vh;
  margin-left: -50px;
}

.st0 {
  fill: none;
  stroke-dashoffset: 3px;
  stroke: red;
  stroke-width: 5;
  stroke-miterlimit: 10;
  stroke-dasharray: 20;
}

<h2>Scroll down this window to draw my path.</h2>
<p>Scroll back up to reverse the drawing.</p>

<svg id="mySVG" viewBox="0 0 60 55" preserveAspectRatio="xMidYMin slice" style="width: 6%; padding-bottom: 42%; height: 1px; overflow: visible">
  <path id="myline" class="st0" stroke-dasharray="10,9" d="M 20 0 v 20 a 30 30 0 0 0 30 30 h 600 a 40 40 0 0 1 0 80 h -140 a 30 30 0 0 0 0 60 h 200 a 40 40 0 0 1 0 80 h -100 a 30 30 0 0 0 -30 30 v 20" /> Sorry, your browser does not support inline SVG.
</svg>

what I want is to animate a <circle> with the growth of the <path> like

I know the path is growing using the strokeDasharray. But still, is there a way to attain what am looking for.? if no then please do suggest another way. thank you..!

Answer 1

Use getPointAtLength()

Looks like another answer already suggested this :)

// Get the id of the <path> element and the length of <path>
var myline = document.getElementById("myline");
var length = myline.getTotalLength();
circle = document.getElementById("circle");
// The start position of the drawing
myline.style.strokeDasharray = length;

// Hide the triangle by offsetting dash. Remove this line to show the triangle before scroll draw
myline.style.strokeDashoffset = length;

// Find scroll percentage on scroll (using cross-browser properties), and offset dash same amount as percentage scrolled
window.addEventListener("scroll", myFunction);

function myFunction() {
  // What % down is it?
  var scrollpercent = (document.body.scrollTop + document.documentElement.scrollTop) / (document.documentElement.scrollHeight - document.documentElement.clientHeight);
  // Length to offset the dashes
  var draw = length * scrollpercent;

  // Reverse the drawing (when scrolling upwards)
  myline.style.strokeDashoffset = length - draw;
  
  //get point at length
  endPoint = myline.getPointAtLength(draw);
  circle.setAttribute("cx", endPoint.x);
  circle.setAttribute("cy", endPoint.y);
  
}

body {
  height: 2000px;
  background: #f1f1f1;
}

#circle{
fill:red;
}

#mySVG {
  position: fixed;
  top: 15%;
  width: 100vw;
  height: 100vh;
  margin-left: -50px;
}

.st0 {
  fill: none;
  stroke-dashoffset: 3px;
  stroke: red;
  stroke-width: 5;
  stroke-miterlimit: 10;
  stroke-dasharray: 20;
}

<h2>Scroll down this window to draw my path.</h2>
<p>Scroll back up to reverse the drawing.</p>

<svg id="mySVG" viewBox="0 0 60 55" preserveAspectRatio="xMidYMin slice" style="width: 6%; padding-bottom: 42%; height: 1px; overflow: visible">
  <circle id="circle" cx="10" cy="10" r="10"/>
  <path id="myline" class="st0" stroke-dasharray="10,9" d="M 20 0 v 20 a 30 30 0 0 0 30 30 h 600 a 40 40 0 0 1 0 80 h -140 a 30 30 0 0 0 0 60 h 200 a 40 40 0 0 1 0 80 h -100 a 30 30 0 0 0 -30 30 v 20" /> Sorry, your browser does not support inline SVG.
</svg>

Answer 2

I'm not sure if you want to just draw a circle or a circle at the end of the line, but maybe getPointAtLength() could help you.

You can get the point at the end the line with myline.getPointAtLength(draw) you can use this to draw a circle at that point

I've added the code to console.log(myline.getPointAtLength(draw)).

My lunch break is just about over, otherwise I'd draw the circle for you too.

// Get the id of the <path> element and the length of <path>
var myline = document.getElementById("myline");
var length = myline.getTotalLength();

// The start position of the drawing
myline.style.strokeDasharray = length;

// Hide the triangle by offsetting dash. Remove this line to show the triangle before scroll draw
myline.style.strokeDashoffset = length;

// Find scroll percentage on scroll (using cross-browser properties), and offset dash same amount as percentage scrolled
window.addEventListener("scroll", myFunction);

function myFunction() {
  // What % down is it?
  var scrollpercent = (document.body.scrollTop + document.documentElement.scrollTop) / (document.documentElement.scrollHeight - document.documentElement.clientHeight);
  // Length to offset the dashes
  var draw = length * scrollpercent;

  console.log(myline.getPointAtLength(draw));

  // Reverse the drawing (when scrolling upwards)
  myline.style.strokeDashoffset = length - draw;
}

body {
  height: 2000px;
  background: #f1f1f1;
}

#mySVG {
  position: fixed;
  top: 15%;
  width: 100vw;
  height: 100vh;
  margin-left: -50px;
}

.st0 {
  fill: none;
  stroke-dashoffset: 3px;
  stroke: red;
  stroke-width: 5;
  stroke-miterlimit: 10;
  stroke-dasharray: 20;
}

<h2>Scroll down this window to draw my path.</h2>
<p>Scroll back up to reverse the drawing.</p>

<svg id="mySVG" viewBox="0 0 60 55" preserveAspectRatio="xMidYMin slice" style="width: 6%; padding-bottom: 42%; height: 1px; overflow: visible">
  <path id="myline" class="st0" stroke-dasharray="10,9" d="M 20 0 v 20 a 30 30 0 0 0 30 30 h 600 a 40 40 0 0 1 0 80 h -140 a 30 30 0 0 0 0 60 h 200 a 40 40 0 0 1 0 80 h -100 a 30 30 0 0 0 -30 30 v 20" /> Sorry, your browser does not support inline SVG.
</svg>